The battle over dioxin contamination in [the Saginaw, Mich.] region had been raging for years when a top [EPA] official turned up the pressure on Dow Chemical to clean it up. On Thursday, following months of internal bickering over Mary Gade's interactions with Dow, the [Bush] administration forced her to quit as head of the U.S. Environmental Protection Agency's Midwest office. Gade told the Tribune she resigned after two aides to national EPA administrator Stephen Johnson took away her powers as regional administrator and told her to quit or be fired by June 1. Gade has been locked in a heated dispute with Dow about long-delayed plans to clean up dioxin-saturated soil and sediment that extends 50 miles beyond its Midland, Mich., plant into Saginaw Bay and Lake Huron. Gade, appointed ... regional EPA administrator in September 2006, invoked emergency powers last summer to order the company to remove three hotspots of dioxin near its Midland headquarters. She demanded more dredging in November, when it was revealed that dioxin levels along a park in Saginaw were 1.6 million parts per trillion, the highest amount ever found in the U.S. Dow then sought to cut a deal on a more comprehensive cleanup. But Gade ended the negotiations in January, saying Dow was refusing to take action necessary to protect public health and wildlife. Dow responded by appealing to officials in Washington, according to heavily redacted letters the Tribune obtained under the Freedom of Information Act. On Thursday, Gade said of her resignation: There's no question this is about Dow. I stand behind what I did and what my staff did. I'm proud of what we did."